The goal of this project is to explore previously-unknown interactions between brain-derived neurotrophic factor (BDNF) and the endocannabinoid system in the cerebral cortex. Both BDNF and endocannabinoids are highly expressed throughout the sensory, motor, and association cortices, and there is a striking overlap of expression of trkB neurotrophin receptors and type 1 cannabinoid (CB1) receptors across cortical layers, with highest levels of expression in cortical layers 2/3 and 5. Disruption f either of these neuromodulatory systems has been implicated in several neurologic and psychiatric diseases, including anxiety, depression, schizophrenia, and seizure disorders, and both systems are currently major targets for the development of novel therapeutics. We found that the effects of BDNF at inhibitory cortical synapses are mediated by the BDNF-induced mobilization of endocannabinoids acting at presynaptic CB1 receptors. The proposed studies will explore the signaling mechanisms underlying BDNF-evoked synthesis and release of endocannabinoids at inhibitory synapses using electrophysiological, molecular biological, and pharmacological approaches. The proposed studies will also extend these findings to examine BDNF-cannabinoid interactions at excitatory synapses, and explore the functional relevance of these interactions in regulating activity-dependent synaptic plasticity. Knowledge gained from these studies will provide insights into the regulation and interdependence of BDNF and endocannabinoid signaling. New mechanistic insights regarding the interaction between these neuromodulators could provide the basis for novel therapeutic approaches to neurologic and psychiatric disease.